I have been using Black Knight Sword since I got it, and upgraded it to +5, I also beat Artorias with it, but it took me a lot of deaths, can anyone recommend a hard hitting weapon that's also fast, any weapon I need to upgrade to match my current one?

i beat my first game with the black knight sword 5 too . the greatlord greatsword has the same attack animation and is slightly stronger. but i'm using the greatsword of artorias which double scale with strength or dex and faith or intel. check out this vid http://www.youtube.com/watch?feature=player_embedded&v=DGBol6QlHZ8

Obsidian Greatsword (Kalameet tail cut). Hard do get without help and does not scale, but has high base damage (320 base, 480 upgraded). *Havn't played str build myself, this was the first weapon I remembered.

For a strength build go with the Demons Greataxe +15, high base damaga S strength staat modifier and enchantable!!! Not very fast but hits like a tank. For a weapon that isnt too slow the claymore is probably best